Contribution to the theory of parachor

Abstract

Deriving theoretically the dependence of the surface tension of a liquid substance, σ, on its density ρ1, the author has arrived by means of a simplified molecular-statistical model, to a temperature-independent product ρ1-1σ1/y, with denominatory in the exponent equal to n/2 + 2/3 (where n is the power of decrease of intermolecular potential energy of attractive forces, with increasing distance). Taking into account the finite gradient of the repulsive forces (exponent n'), we obtain an additional relatively small correction in a positive sense. The value resulting hence for γ, in the case of the individual real compounds, is in average close to 4 - in agreement with the empirical formula of the Sugden parachor representing a temperature-invariant quantity. This quantity is subjected to the theoretical analysis from the point of view of its applicability to investigation of the chemical constitution of substances in solutions, in terms of the additivity principle assumed by Sugden. As a result of this analysis, a concept is intriduced of the apparent parachor of a solute, IIi, (as a quantity experimentally accessible) - in analogy to its apparent volume φi.